Mircro-electromechanical systems (MEMS) exist which combine mechanical devices, such as mirrors and actuators, with electronic control circuitry for controlling the mechanical devices. One such device is referred to as a diffractive light device (DLD), and includes a variable capacitor composed of a fixed reflective ground plate and a semi-transparent, electrostatically movable second plate. The variable gap between the plates produces a desired interference or diffraction of light passing therein, which can be used for spatial light modulation in high resolution displays and for wavelength management in optical communication systems.
Conventional control systems for controlling the variable gap in DLDs and other MEMs devices, however, have been shown to have a non-linear relationship between the voltages generated to control the gap size versus plate displacement for achieving a desired gap size. This non-linear relationship limits precise control of plate movement to less than one third of the total gap distance before the plate “snaps down” to mechanical stops. This “snap down” phenomenon is also known as a pull-in characteristic in the art.
Techniques for increasing the controllable distance often require large control circuit footprints due in part to the presence of switching elements and the like, which correspondingly increases the footprint of the controller and prevents implementation in applications requiring relatively small control circuit sizes (e.g., not greater than 20 u2 per MEMs device). Other techniques for increasing the controllable distance suffer from parasitic drops in control lines (particularly in arrayed DLD applications), which causes a variation in power to DLDs across the array.